POLIOMYELITIS

1. POLIOMYELITIS

2. AGENT FACTORS: Agent: Poliovirus, - RNA virus, serotype –1,2,3 - Most outbreaks – type 1 -Survive for long periods in external environment in cold climate - Can live in water for 4 mnths & faeces for 6 mnths - hence faecal – oral route

3. Reservoir of infection: • Man is the only known reservoir • Most are subclinical cases, no chronic carrier, no animal carriers • Mild & subclinical cases plays an important role in spread of infection • Submerged part in iceberg phenomenon • For every clinical case- 1000 children and 75 adult subclinical cases

4. Infectious material: • Faeces and Oro-pharyngeal secretions of an infected person Period of communicability: • Cases are most infectious 7 to 10 days before and after onset of symptoms • In faeces the virus is excreted for 2 to 3 wks & can go on for as long as 3 – 4 mnth

5. HOST FACTORS: Age: • occur in all age groups • Children are more susceptible than adults • Most vulnerable age is between 6 months to 3 years in India Sex: M:F, 3:1

6. Risk factors: Paralytic polio in an individual who have been already infected with polio virus, has been found to precipitated by factors like - • fatigue, trauma, intra muscular injections, operative procedures esp. during epidemics of polio, immunizing agents particularly alum containing DPT

7. Immunity: • Infection with one type does not offer complete protection against other two type of viruses • Neutralizing Ab’s - index of immunity to polio after infection Environmental factors: • More seen to occur in rainy season • Sources are contaminated water, food, flies • Overcrowding and poor sanitation provides opportunities for exposure to infection

8. Mode of transmission: • Faecal-oral route – developing countries • Droplet infection – developed countries, acute phase of disease Incubation period: 7-14 days(range 3-35 days) Clinical spectrum: • Inapparent (subclinical) infection • Abortive polio or minor illness • Non paralytic polio • Paralytic polio

9. a) Inapparent (subclinical) infection: • Occurs in approx. 91-96% infections • No symptoms • Recognized only by virus isolation or rising antibody titres b) Abortive polio or minor illness: • Occurs in 4-8% of infections • Causes only mild or self limiting illness • Patient recovers quickly • Recognized only by virus isolation or rising antibody titres

10. c) Non paralytic polio: • Occurs in 1% of all cases • s/o: stiffness and pain in neck and back • Disease lasts 2 to 10 days • Recovery is rapid • It is synonymous to aseptic meningitis

11. d) Paralytic polio: • Occurs in less than 1% cases • Invades CNS & causes paralysis of varying degree • Predominant sign – Asymmetrical flaccid paralysis (AFP) • If fever at time of onset of paralysis – polio suspected • Other symptoms - malaise, anorexia, nausea, vomiting, abdominal pain, sore throat, head ache and constipation

12. Signs: • stiffness of neck & back muscles • Tripod sign • Descending paralysis – hip to downwards • Asymmetrical patchy paralysis • DTRs are diminished before onset of paralysis • Progression of paralysis to reach its maximum in majority cases occurs in less than 4 days • No sign of sensory loss

15. Cranial nerve involvement seen in bulbar and bulbo spinal forms of paralytic polio • Facial asymmetry, difficulty in swallowing, weakness of voice • Respiratory insufficiency can be life threatening & is usually cause of death • Atrophy of muscles also seen • Progressive paralysis, coma & convulsions indicate diagnosis other than polio Treatment: • No specific treatment • Physiotherapy and good nursing care from beginning can minimize/ prevent crippling

18. Prevention: • Immunization is the most effective method • Two types of vaccine: • Inactivated polio vaccine(IPV)/ Salk • Oral polio vaccine(OPV)/ Sabin

20. Inactivated polio vaccine(IPV)/ Salk: • Given i/m (preferred) or s/c injection • Stable at ambient temperature, but should be refrigerated to ensure no loss of potency • Freezing should be avoided • Primary course of immunization consist of 4 inoculations • Available as stand alone product or in combination form • Induces humoral antibody and not intestinal/ local immunity

21. IPV protect individual from paralytic polio, but do not prevent re-infection of gut by wild polio viruses • Hence it does not offer any benefit for the community as wild virus can multiply in gut and be a source of infection to others • It is unsuitable during epidemic because: • Immunity is not rapidly achieved, more than one dose required to induce immunity • Injections are to be avoided during epidemics as they may precipitate paralysis

22. Advantages: • Can be given in immuno compromised and pregnant women Associated risks: • No serious ADRs except minor local erythema, induration and tenderness

23. Oral polio vaccine(OPV)/ Sabin: • Described by Albert Sabin in 1957 • Contains live attenuated vaccine (type 1,2,3) National immunization schedule: • Primary course of 3 doses at 1 month interval • Starting at 6 wks and followed by 10 & 14 wks • Zero dose is recommended at birth • All infants should vaccination before 6 months of age as most polio cases occur between 6 months to 3 years period • One booster dose of OPV is given at yrs

25. Dose & mode: 2 drops, orally Development of immunity: • IgA produced in intestine prevent subsequent infection of alimentary canal with wild polio, thus preventing spread in community • OPV induces both local & systemic immunity • Vaccine progeny excreted in faeces 2* spread to household contact & susceptible host in community Herd immunity established • This property eliminates wild polio from the community & replace it with attenuated strain

26. Advantages: • Easy to administer • Doesn't require highly trained personnel • Induce both humoral and intestinal immunity • Even single dose elicits substantial immunity • Herd immunity • Useful in controlling epidemics • Relatively inexpensive

27. Complications: • VAPP(vaccine associated paralytic poliomyelitis)----due to type 3 strain Containdications: • All live vaccines are C/I in immuno compromised patients and pregnant women • IPV given in immuno compromised if necessary

28. Storage: A) stabilized vaccine – recent vaccines are heat stabilized by adding magnesium chloride in it • Can be kept for a year at 4* C & for a month at 25*C with out loosing potency B) Non stabilized vaccine – Vaccine sould be stored at -25*C in deep freezer • Vaccine vial kept in ice at field level during administration to children

29. Sequential administration of IPV & OPV: • In some countries sequential schedule of 1 – 2 dose of IPV followed by > 2 doses of OPV has been adopted • This approach reduce the event or even prevent VAPP, while giving both systemic and local immunity

30. Differences between IPV & OPV IPV(Salk) • Killed virus • Given s/c or i/m • Only humoral immunity, no local immunity • More difficult to manufacture OPV(Sabin) • Live attenuated • Orally • Both humoral & intestinal immunity • Easy to manufacture

31. IPV • Prevent paralysis, but do not prevent re-infection with wild polio • Not useful in epidemics • Virus content is 10,000 times more than OPV, Costlier • Doesn't require stringent condition during storage & transportation OPV • Prevent paralysis and also intestinal re-infection • Can be used in epidemics • Cheaper • Required to be stored & transported in sub zero temperature

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